(a) Field of the Invention
The present invention relates to a compact zoom lens system and, more particularly, to a compact zoom lens system for photographing of which the zoom ratio is 2.
(b) Description of the Prior Art
The zoom lens system disclosed in Japanese published unexamined patent application No. 111013/83 is known as a zoom lens system comprising a first lens unit having negative refractive power and arranged as a movable lens unit, a second lens unit having positive refractive power and arranged as a movable lens unit, and a third lens unit arranged as a fixed lens unit. However, the above-mentioned known zoom lens system has disadvantages described below.
That is, in case of said known zoom lens system, the third lens unit is arranged as a meniscus lens which is convex toward the object side. Therefore, flare caused by offaxial rays becomes unfavourable, and the intensity of light in the marginal portion becomes insufficient.
Besides, the marginal portion of the third lens unit comes to a position closer to the film side. Therefore, to prevent the third lens unit from interfering with the mirror when said known zoom lens system is used with a single-lens reflex camera, it is necessary to locate the third lens unit at a somewhat long distance from the film surface. Consequently, it is impossible to make the overall length of the lens system satisfactorily short, and the lens system as a whole cannot be made compact.
Furthermore, as the apex of the third lens unit comes to a position closer to the object side, the moving range of the second lens unit should be shifted toward the object side. This also means that it is impossible to make the overall length of the lens system short.